Distillation of a fluid mixture, e.g. air, into two or more portions enriched in a respective mixture component, has generally been carried out employing one or more distillation columns which employ trays or random packing as the column internals or mass transfer elements.
Recently there has developed an increasing use of structured packing as mass transfer elements in distillation columns because structured packing has a lower pressure drop than trays and has more predictable performance than random packing.
However, in a column having more than one section, especially where the hydraulic loads in one section are substantially different from the hydraulic loads in another section, there is a problem because the hydraulic load variations cause one or more sections to be much closer to flooding than other sections. This imposes a severe operating limitation on the columns and significantly reduces the degree of product flowrate variation that can be achieved without risking flooding or other malperformance. While the problem may be addressed by changing the column internal diameter in each section, such a solution is quite costly.
Accordingly it is an object of this invention to provide a method and apparatus for the cryogenic separation of air comprising a column which uses structured packing column internals and has improved operating flexibility over known systems.